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Re: [libvirt] [RFC] Data in the <topology> element in the capabilities XML



On 01/17/13 16:43, Daniel P. Berrange wrote:
I beg to differ:

"This technology is informally called CMT (Clustered Multi-Thread)
and formally called "module" by the AMD's marketing service, but
whose real name is "Clustered Integer" Core Technology. In terms of
hardware complexity and functionality, this "module" is midway
between a true dual-core processor and its integer power (each
thread having a fully independent integer core) and a single core
processor that has the SMT ability, which can create a dual threads
processor but with the power of one (each thread shares the
resources of the core with the other thread)."

(source: http://en.wikipedia.org/wiki/Bulldozer_(microarchitecture)#BULLDOZER_Core_.28aka_Module.29
)

oVirt/vdsm considers the "Module" as a core with two threads, where
others consider it more as separate cores. The performance depends
on the type of task that is being run on the module.

So what information does VDSM use to identify this hardware topology.


VDSM uses the <topology> element (subelement of cpu) in the capabilities and multiplies the numbers by the number of numa nodes. As the data there is taken from nodeinfo, this breaks on some systems.


In some form or another we need to be providing the more detailed and
accurate topology infomation in the capabilities NUMA description.

What does 'hwloc --no-io --no-caches' shown on a Bulldozer machine ?

# hwloc-info --no-io --no-caches
depth 0:	1 Machine (type #1)
 depth 1:	2 Socket (type #3)
  depth 2:	4 NUMANode (type #2)
   depth 3:	32 Core (type #5)
    depth 4:	32 PU (type #6)

hwloc recognizes it as cores ...

# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                32
On-line CPU(s) list:   0-31
Thread(s) per core:    2
Core(s) per socket:    8
Socket(s):             2

... lscpu as as threads ...

NUMA node(s):          4
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 1
Stepping:              2
CPU MHz:               1400.000
BogoMIPS:              4389.80
Virtualization:        AMD-V
L1d cache:             16K
L1i cache:             64K
L2 cache:              2048K
L3 cache:              6144K
NUMA node0 CPU(s):     0-7
NUMA node1 CPU(s):     8-15
NUMA node2 CPU(s):     16-23
NUMA node3 CPU(s):     24-31



Daniel



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